Combustion Flashcards
If only 2 units of oxygen are required for complete combustion of 1 unit of methane, why must 10 units of air be supplied for complete combustion of 1 unit of methane
There are 2 units of oxygen in 10 units of air
An inspirated burner is found on a?
Natural draft appliance
What force makes stack action possible
Buoyancy
A flame with a two part cone is developed by what type of burner
Pre mix burner
What is the maximum equivalent length of a combustion air duct ducting allowed without increasing the size
20 feet
Combustion air sizing is taken from the appliances ———?
Input rating
Define the term combustion
The rapid oxidation of fuel resulting in the production of heat or heat and light
When gas burns properly, the hydrogen combines with the oxygen of the air to produce—————-, the carbon combines with the oxygen to produce————- and the ————— in the air passes through the flame unchanged.
Water vapour
Carbon dioxide
Nitrogen
Define combustion air
The air required to completely burn the fuel
Define primary air
Air required for the initial stages of the combustion process and is mixed with the fuel prior to combustion
Define secondary air
Air required for the intermediate and final stages of the combustion process and is mixed with the fuel prior to combustion
Define excess air
Air supplied for the combustion process in excess of, but not required theoretically
Define combustion products
Constituents resulting by uniting the fuel with oxygen, usually thought of as being gas, primary air or secondary air
Define range of flammability
The percentage of gas present in a gas/ air mixture between the upper and lower limits that will burn
Define incomplete combustion
Combustion that does not convert all the carbon and or hydrogen into water vapour and or carbon dioxide
Define lift off
The gas/air mixture speed exceeds the flame speed resulting in a flame that burns too high above the burner
Define flashback
The gas/air mixture is slower than the flame speed causing the flame to burn inside the burner, possibly at the orifice
What 3 components are required for combustion
Fuel
Heat (ignition)
Oxygen (air)
What product creates concern when incomplete combustion occurs
Carbon monoxide (Co)
What flame color is most likely to indicate poor combustion
Yellow
What flame color usually indicates dust or dirt passing through the flames
Orange
What colour of flame indicates good combustion
Blue
What are the two constituents of the products of combustion that can form due to incomplete combustion of fuel
Aldehydes and carbon monoxide
A compound that consists of only hydrogen and carbon would be a definition of?
Hydrocarbon
What condition produces upward flow of vent gasses in a natural draft appliance
Chimney effect
What does the term Venturi principle mean
Partial vacuum due to fluid flow through a narrow opening
What is the range of flammability of a fuel
The amount of fuel/air mixture that will burn
Define the heating value of fuel
The heat in a volume of fuel that is released by combustion
What does lp refer to as fuel
Liquified petroleum gasses
What controls the amount of air that can enter an atmospheric burner
Air shutters
What are the products which result from complete combustion of the reactants oxygen and methane
Carbon dioxide and water vapour
What three conditions are needed for combustion to take place
Oxides, fuel , heat
What are the three mechanisms by which heat is transferred
Radiation, conduction, convection
Which type of heat can easily be focused
Radiation
How does latent heat differ from sensible heat
Latent heat does not change the temperature of a substance
What is the difference between heat and temperature
Heat is energy, temperature is a specific point on a thermostat
What is specific heat
Energy needed to warm a specific volume of a substance by one degree
How does a metallic object become warmer by heating it from one end only
Heat energy conducts from molecule to molecule through the metal
Which form of latent heat changes propane liquid to propane gas
Vaporization
What are two different names for a non aerated flame
Luminous flame or non linting flame
Which type of flame is a Bunsen flame
Aerated flame
What are the two main burner classes
Atmospheric and forced draft
Why are ports of induced draft burners larger than ports of natural draft burners
To reduce flow restriction through the burner
Why does the induced draft appliance use a fan on the outlet of the appliance
To overcome the resistance of the heat exchanger to the flow of products of combustion through it
Why do some burners have flame deflectors
To prevent hot spots in the combustion chamber
How is temperature measured
Thermometer
What temperature in Fahrenheit is represented by a temperature of 273 Celsius
273x1.8+32 = 523.4 Fahrenheit
Why are gas infrared heaters becoming so popular
Heat is not wasted by warm air lost to outdoors when overhead doors are open
What approximate percentages of combustion air are primary air and secondary air
60% and 40%
Why is the production of carbon monoxide from an appliance such a concern
It accumulates in the blood and asphyxiates
